1. Field of the Invention
This invention relates to loading, transportation and delivery of compressed gas such as compressed natural gas and more particularly, to a free piston compressed natural gas delivery apparatus and method for operating the apparatus. In a preferred embodiment, the free piston gas delivery apparatus includes one or more gas-filled cylinders, each fitted with a free piston and mounted on a truck or other vehicle, and at least one water-filled cylinder, also mounted on the vehicle, along with appropriate piping to facilitate coupling the gas-filled cylinders to a receiving reservoir and sequentially introducing water or other working fluid on the opposite side of the free piston from the gas in each cylinder and forcing the piston along the interior of the cylinder to displace the gas from the cylinder to the reservoir. Alternatively, tap water from any available source can be pumped into the cylinders according to the invention.
Due to current expensive and unreliable methods for transporting supplies of natural gas, oil and other petroleum products from various countries to the United States, the U.S. government is encouraging conversion of motor vehicles from gasoline to gaseous fuels such as compressed natural gas, or methane. If such a conversion could be effected in an economical manner, these vehicles, which include school bus fleets, passenger cars, trucks, buses and all other vehicles currently operating on gasoline or diesel fuel would be candidates for conversion to operation by compressed natural gas. However, a primary problem which arises in using compressed natural gas for powering motor vehicles is the fact that the user vehicle must be fueled to a pressure of about 2000 psi with compressed natural gas in order to obtain a practical driving range. If the delivery vehicle is restricted to a pressure under or about 4000 psi and is adapted to facilitate "bleeding" of the compressed natural gas from the delivery vehicle into the user vehicle, the resulting pressure in both the user vehicle and the delivery vehicle would be about 2000 psi. Accordingly, this transfer would facilitate delivery of only approximately one-half of the compressed natural gas carried in the delivery vehicle, an extremely inefficient mode of transfer. The problem is exacerbated under circumstances where an intermediate reservoir such as a tank or reservoir at a service station must be initially filled by the delivery vehicle and subsequently used to fill multiple user vehicles on an individual basis, in conventional fashion. Under these circumstances, the delivery vehicle might typically deliver compressed natural gas to the intermediate service station reservoir at a pressure of about 3000 psi. Accordingly, only about one-fourth of the compressed natural gas carried in the delivery vehicle could then actually be delivered to the user vehicle. Inefficiency of the transfer system is readily apparent, first, because delivery of one-fourth of the compressed natural gas originally loaded on the delivery truck is not cost-effective from the standpoint of useful freight, considering the weight of the cylinders and other equipment which must be hauled to the delivery point, and secondly, the time required for the delivery process becomes prohibitive as the pressure in the compressed natural gas truck slowly approaches the pressure in the receiving reservoir.
2. Description of the Prior Art
One of the techniques used to overcome the compressed natural gas delivery inefficiencies noted above involves using compressors located either on the compressed natural gas delivery truck or at the receiving station, to transfer the compressed natural gas from one reservoir to another. This facility allows delivery of a large quantity of the compressed natural gas transported in such a delivery truck, but the large amount of time required for compression and delivery becomes a major detrimental factor. Accordingly, both trucks and drivers are immobilized during the delivery sequence for long periods of time and the number of deliveries per day for each truck is seriously curtailed.
Pertinent prior art patents are as follows: U.S. Pat. No. 3,282,305, dated Nov. 1, 1966, to J.P. Antolak, entitled "Cylinder Filling Apparatus"; U.S. Pat. No. 4,649,968, dated Mar. 17, 1987, to B. J. Berrettini, entitled "Automatic Precision Liquid Loading Control System"; U.S. Pat. No. 3,812,888, dated May 28, 1974, to Charles R. Dalton, entitled "Compressed Liquid Gas Filling System"; U.S. Pat. No. 4,805,674, dated Feb. 21, 1989, to R. E. Knowlton, entitled "Natural Gas Storage and Retrieval System"; and U.S. Pat. No. 4,987,932, dated Jan. 29, 1991, to Robert M. Pierson, entitled "Process and Apparatus for Rapidly Filling a Pressure Vessel With Gas".
It is an object of this invention to provide a method and apparatus for delivering compressed gas, and compressed natural gas in particular, to a receiving reservoir from a cylindrical reservoir containing a free piston, by containing the gas on one side of the piston and displacing the gas from the reservoir by operation of the piston using a substantially incompressible fluid injected into the reservoir on the opposite side of the piston.
Another object of this invention is to provide a new and improved free piston gas delivery apparatus for delivering compressed gas such as compressed natural gas from a cylindrical reservoir having a sliding free piston, wherein the compressed natural gas is located on one side of the free piston and a substantially incompressible fluid such as water is pumped into the opposite side of the free piston to force the compressed natural gas from the reservoir by movement of the piston longitudinally along the interior of the cylindrical reservoir.
Still another object of this invention is to provide a free piston gas delivery apparatus which is characterized by one or more cylindrical, high pressure gas cylinders, each fitted with a free piston and appropriate plumbing for temporarily storing compressed natural gas on one side of the free piston and facilitating the sequential introduction of water on the opposite side of the free piston to displace the compressed natural gas from the cylinders by operation of the free piston.
Yet another object of this invention is to provide a method for transporting and delivering a compressed gaseous product such as compressed natural gas, which method includes the steps of loading the compressed natural gas into multiple, longitudinally tilted, cylindrical tanks or reservoirs containing a free piston, transporting the cylinders and compressed natural gas to a desired location for emptying into a receiving reservoir, introducing a substantially incompressible fluid such as water from a water storage cylinder sequentially into one end of the cylindrical reservoirs on the opposite side of the free piston from the compressed natural gas at a pressure greater than the pressure of the compressed natural gas and forcing the compressed natural gas from the cylindrical reservoirs into the receiving reservoir by operation of each free piston.